1. Field of the Invention
The invention relates to the field of charge-coupled devices (CCD) particularly charge-coupled memories.
2. Prior Art
Charge-coupled devices for a number of years have been investigated and used, particularly experimentally, for memories, video displays and other applications. For a discussion of CCD technology and its applications, see "Charge-Coupled Devices -- A New Approach to MIS Device Structures," IEEE Spectrum, July 1971, by Boyle and Smith, beginning at page 18.
One application for charge-coupled devices has been semiconductor memories, particularly those employing metal-oxide-silicon (MOS) technology. For example, a plurality of charge-coupled recirculating shift registers have been employed for fabricating serial memories. While these memories have considerably slower access times than most random-access-memories employing MOS technology, they nonetheless fill the gap, in terms of cost per bit of storage, between the fast access time RAMs and memory systems employing magnetic disks and tapes. For an analysis of the costs versus access times for various memories, see "Charge-Coupled Devices Move in on Memories and Analog Signal Processing," Electronics, Aug. 8, 1974 by Laurence Altman, beginning on page 91.
CCD memories are capable of being fabricated at lower cost (in terms of cost per bit of storage) when compared to other semiconductor memories because higher CCD densities are possible. Typically in the fabrication of semiconductor memories yields are not directly affected by density, and hence higher densities generally result in less costly memories.
In order to achieve these higher densities for CCD memories circuit topology or layout becomes an important consideration in the design of a memory. The present invention discloses a unique arrangement for recirculating shift registers employed in a CCD memory which provides a highly efficient layout. In the presently preferred embodiment the design is utilized to fabricate a 16K memory.